1. Field of the Invention
The present invention relates to a linear guide apparatus in which inclined portions are formed at both end portions of a slider-side rolling element raceway groove which makes up a rolling element rolling path.
2. Description of Related Art
A linear guide apparatus in which a guided body is guided in a straight line while infinitely circulating rolling elements such as rollers or balls is one of important mechanical elements which affect largely a kinetic accuracy of semiconductor manufacturing systems, ultra-precision machine tools and ultra-precision measuring equipment.
The linear guide apparatus is an apparatus which includes a guide rail having a rail-side rolling element raceway groove provided thereon and a slider main body having a slider-side rolling element raceway groove provided thereon so as to face the rail-side rolling element raceway groove and supported on the guide rail so as to move in axial directions by virtue of rolling of a plurality of rolling elements which are provided within a rolling element rolling path which is formed between the slider-side rolling element raceway groove and the rail-side rolling element raceway groove. This apparatus includes a rolling element return path which is provided within the slider main body so as to extend parallel to the rolling element rolling path and direction turning paths which are provided in end caps mounted at both end portions of the slider main body in moving directions thereof so as to each establish a communication between the rolling element rolling path and the rolling element return path.
When the rolling elements of the linear guide apparatus are endlessly circulated along the rolling element rolling path, the direction turning paths and the rolling element return path, periodic minute vibrations (hereinafter, referred to as rolling element passing vibrations) are generated, whereby the kinetic accuracies of the aforesaid system, machine and equipment are largely affected. The rolling element passing vibrations are caused to appear when the rolling elements which roll in the rolling element rolling path (loaded area) while being loaded by a pre-load or external load roll out of the loaded area to the rolling element circulation path (unloaded area), whereby the load on the rolling elements is released or, on the contrary, when the rolling elements enter the loaded area from the unloaded area, whereby load is applied again to the rolling elements.
In order to suppress the rolling element passing vibrations, slopes referred to as crownings are provided at both end portions of the slider-side rolling element raceway groove which makes up the rolling element rolling path so as to make a change in load which happens as the rolling elements enter and emerge from the rolling element into and out of the loaded area occur gradually, thereby making it possible to reduce rolling element passing vibrations.
Here are two types of linear guide apparatuses; a linear guide apparatus in which only crownings are formed at both end portions of a slider-side rolling element raceway groove, and a linear guide apparatus in which crownings and chamfers are both formed at both end portions of a slider-side rolling element raceway groove.
As an example of the linear guide apparatus in which only the crownings are formed at both end portions of the slider-side rolling element raceway groove, there is a linear guide apparatus in which only crownings which are each made up of a less steeply inclined slope which extends into a single arc-like shape while neighboring a slider-side rolling element raceway groove and a steeply inclined slope which extends into a straight line while neighboring the slope so as to suppress the reduction in rigidity, thereby making it possible to suppress the amplitude of rolling element passing vibrations to as small a value as possible (for example, Japanese Patent Unexamined Publication No. JP-A-2005-337455).
In addition, as another example of the linear guide apparatus in which only the crownings are formed at both end portions of the slider-side rolling element raceway groove, there is a linear guide apparatus in which a crowning is configured into a curve such as a power function curve, a curve made up of a plurality of curves and a least square method curve, and in which rigidity relative to any one direction of a perpendicular direction (vertical direction), a horizontal direction and a rolling direction of the slider main body is held substantially constant and rigidity relative to either or both of a pitching direction and a yawing direction of the slider main body is held substantially constant (for example, Japanese Patent Unexamined Publication No. JP-A-2003-035314).
On the other hand, as the linear guide apparatus in which crownings and chamfers are both formed at both end portions of the slider-side rolling element raceway groove, there exist a linear guide apparatus in which a linearly extending crowning and a chamfer, which extends in a straight line between the crowning and an end face of a slider main body, are formed (for example, Japanese Patent Unexamined Publication No. JP-A-2005-273765) and a linear guide apparatus in which a curvedly extending crowning and a round-shaped (or rounded) chamfer, which is formed between the crowning and an end face of a slider main body, are formed to thereby suppress not only the occurrence of element passing vibrations but also the reduction in rigidity, so as not only to enhance the durability of end caps when the linear guide apparatus is driven at high speeds but also to reduce the level of noise and vibration (for example, Japanese Patent Unexamined Publication No. JP-A-2006-029384 and PCT Application Publication No WO2005/019668) Here, the crowning of JP-A-2006-029384 includes a curved effective crowing portion which continues from a rolling surface of a rolling element rolling path and a curved out-of-effect crowning portion which continues to the effective crowning portion, and a crowning depth of the effective crowning portion is of the order of an elastic deformation amount of a rolling element that is generated when a pre-load is applied.
Furthermore, as another example of the linear guide apparatus in which crownings and chamfers are both formed at both end portions of the slider-side rolling element raceway groove, there exists a linear guide apparatus in which crownings are formed at both ends of a loaded area relative to a loaded rolling surface, and stepped portions of the order of 5% of a diameter of a rolling element are formed at edge portions of the loaded rolling surface so as to be lower than an inside diameter-side side wall surface of a direction turning path (for example, Japanese Patent Unexamined Publication No. JP-A-2002-155936).
However, in the above five Japanese Patent Unexamined Publications and PCT publication, which have been described above, have the following inherent problems.
In the JP-A-2005-337455, when the diameter of a rolling element is 4 mm, a maximum depth of the crowning, which is made up of the slope which extends into the single arc-like shape and the slope which extends in the straight line, is set to be on the order of 20 μm. In general, when the diameter of the rolling element is 4 mm, the direction turning path has a clearance of the order of 0.1 to 0.4 mm relative to the rolling elements for easy circulation thereof, and a stepped portion is generated by a difference in level of the order of 0.05 to 0.2 mm, corresponding to a half of the clearance, which is generated between the rolling surface of the rolling element rolling path and a guide surface of the direction turning path. Even though the maximum depth of the crowing is 20 μm, the difference in level is generated between the rolling surface of the rolling element rolling path and the guide surface of the direction turning path, and when the linear guide apparatus is driven at high speeds, the rolling elements are brought into collision with the stepped portions, causing a fear that damage such as peeling is caused to occur at the end portions of the rolling element rolling path in an early stage of the life of the linear guide apparatus.
In addition, in the JP-A-2003-035314, (estimating from FIGS. 7 and 13 thereof) the maximum depth of the crowning is a small value in the range of 10 μm to 20 μm, and as in the case of the JP-A-2005-337455, when the linear guide apparatus is driven at high speeds, the rolling elements are brought into collision with stepped portions, which are caused by similar differences in level, causing a fear that damage such as peeling is caused to occur at the end portions of the rolling element rolling path in an early stage of the life of the linear guide apparatus.
Additionally, in the JP-A-2005-273765, the round-shaped chamfer formed between the crowning and the end face of the slider main body protrudes further than the guide surface of the direction turning path, so as to intentionally bring the rolling elements into collision with the round-shaped chamfer. However, since this round-shaped chamfer has to have a radius of curvature of 0.1 mm or greater and be formed into a mirror surface configuration, ultra-precision grinding work is required, causing a problem with working costs. In addition, the crownings and the round-shaped chamfers are machined in separate steps. Therefore, a tremendous amount of labor hours need to be spent inspecting to confirm that a boundary portion between the crowning and the round-shaped chamfer is formed into a shape made up of a curved surface and having no angled portion and has a radius of curvature of 0.1 mm or greater.
In addition, in the JP-A-2006-029384, when the linear guide apparatus is driven at high speeds, when entering the rolling element rolling path which is the loaded area from the direction turning path, the rolling elements are brought into collision with the out-of-effect crowning portion which continues to the effective crowning portion to thereby generate stress Since the out-of-effect crowning portion is formed into the curved shape, although the stress is mitigated, compared to a sharp edge or a minute round shape, since the rolling elements and the out-of-effect crowning portion are both made up of convex surfaces, the effect of stress mitigation is reduced.
Furthermore, in the WO2005/019668, the axial length of the round-shaped chamfer is increased to increase the radius of curvature thereof, so as to mitigate stress generated by the collision of the rolling elements. However, adopting this configuration decreases an area where the inner circumferential guide member which makes up the inner circumferential guide surface of the direction turning path and the end face of the slider main body, whereby a recess portion is formed between the inner circumferential surface of the inner circumferential guide member and the chamfer, and depending on the posture of the mounted linear guide apparatus, there is caused a fear that the rolling elements fall in the recess portion to thereby interrupt a smooth rolling operation thereof.
Moreover, in the JP-A-2002-155936, since the stepped portion is formed in such a manner that the edge portion of the loaded rolling surface becomes lower than the inside diameter-side side wall surface of the direction turning path, when the rolling elements roll into the direction turning path from the rolling element rolling path, the stepped portion interrupts the circulation of the rolling elements, causing a fear that the rolling elements are prevented from smooth rolling operation. Because of this, the molding accuracy of components and machining accuracy of the slider main body need to be enhanced, and this increases the number of steps including inspections, causing a problem that the productivity is deteriorated.